The enhanced physical downlink control channel (E-PDCCH) has been discussed in 3GPP as a potential technical solution to enhance the PDCCH coverage and capacity. The fundamental requirements of the E-PDCCH lie in not only supporting beamforming on a PDCCH, but also supporting multi-user multi-input/multi-output (MU-MIMO). However, it will bring two problems, i.e., inter-cell interference (ICI) caused by the beamforming, and multi-user interference (MUI) caused by the multi-user multi-input/multi-output. Due to the instability of the MUI and ICI, for example, a change of the ICI within 5 ms may exceed 20 dB over some bandwidths, which is hardly to be predicted such that it is almost impossible for a PDCCH to select an appropriate aggregation level to guarantee a target block error rate (BLER).
In order to guarantee the target block error rate, a plurality of encoding rates might be required, one of which is based on the aggregation level of control channel elements (CCEs). A CCE is composed of 9 resource element groups (REG), each being composed of 4 resource elements. In the prior art, four CCE aggregation levels are prescribed, i.e., N=1, 2, 4, 8. These four CCE aggregation levels play a role of cyclically and repetitively encoding. However, it is hard for an eNodeB to predict the magnitude of MUI and ICI on the next PDCCH. Therefore, it would be impossible to provide an appropriate aggregation level to guarantee the target BLER. Because PDCCH resources are very important, it is required to select an appropriate aggregation level to cancel the MUI and ICI on the PDCCH. Once the MUI and ICI on the PDCCH are cancelled, the problem of instable interference on the PDCCH will be resolved.